An ongoing goal in the filtration industry is to perform filtration continuously for sustained periods, even when processing fluids with high amounts of solids or colloidal materials. A wide variety of filter media designs and configurations have been used in attempts to provide a continuous filtration process. This goal has led to several known techniques for continuously inhibiting the buildup of scale, cake or films which tend to deposit on and block passage of desired fluid flow through associated filter media. In some cases, these techniques are used intermittently, to perform what is called cyclic cleaning of filter media surfaces, usually when an associated filtration process has been suspended for such cleaning.
In order to achieve sufficient surface area to serve in commercial scale filtration applications, multiple layers of filter media such as flat sheet membranes are often collected together within a single filtration device. Combining a plurality of sheet membranes may include arranging them in parallel stacks, mounted either horizontally or vertically, or, winding a relatively long single sheet into a spiral configuration.
Various techniques for continuous and cyclic cleaning of associated filter media have been used. U.S. Pat. Nos. 4,872,988; 4,952,317; 5,014,564 and 5,725,767 teach using reciprocating torsional vibration applied parallel to planes of stacked filter elements. Flat filter leaf elements may be stacked within and rigidly attached to a pressure vessel, whereby the entire filtration device is torsionally shaken in a back and forth or reciprocating manner generally parallel to the face of the leaf elements and orbitally around a vertical axis through the center of the stack. These reciprocating orbital shaking motions may produce boundary layer turbulence or interference on upstream surfaces of each membrane or leaf element to continuously scour associated surfaces of any scaling, cake or film. In order to transmit and to withstand the relatively violent motions being applied by external vibration devices, the leaf elements may include a support mounted at an interior surface of the associated membrane. The membranes may be sealed or laminated to each other over a support element or plate. The support element may be constructed of a relatively rigid plastic material, metal or other suitable materials.
U.S. Pat. No. 6,322,698 teach vibratory cleaning by applying reciprocating torsional vibration parallel to the planes of stacked flat filter elements. The flat filter elements includes frame elements, multiply-stacked, with outer edges sealingly combine to form an integral pressure vessel. The entire stacked frame device may be torsionally shaken parallel to the planes of the filter elements. This shaking motion may produce boundary layer scouring for the purpose of preventing accumulation of surface scaling, caking or filming on upstream surfaces of associated filter media.
U.S. Pat. No. 6,287,467 teaches cleaning parallel mounted, flat leaf filter elements using air bubbles forcefully directed between and sweeping across the upstream surfaces of their filter leaf elements. A solid plate-like stiffening element may be disposed parallel to the filter media of each element to provide overall stiffness with desired spacing between upstream surfaces through which cleaning air bubbles are directed. Conventional filter element design and construction often includes rigid support structures with internal reinforcing plates and/or rigid mechanical elements disposed within the central work area of such filter elements